Nanometer scale particles made up of metals typically found in semiconductor materials are generally referred to as quantum dots (QDs). Quantum dots of the same material, but of different sizes, can emit light of different colors. Surface modification of QDs with organic polymers allows one to tailor their properties and incorporate the particles into larger materials. QDs are currently used in numerous electronic and biological applications.
Quantum dots that display properties of Type-II band semiconductor materials are described in Kim et al., J. Am. Chem. Soc 125, 11466-11467 (2003). See also U.S. Pat. No. 7,390,568. Type-II QDs are expected to have useful properties because of the spatial separations of electron charge carriers. Type-II structures can allow access to wavelengths that would otherwise not be available with a single material. In addition, the separation of charges in the lowest excited states of type-II nanocrystals makes these materials more suitable in photovoltaic or photoconduction applications. Thus, there is a need to identify improved Type-II QDs.